Neighbors Caused Me Over $1000 In Expenses Due To Negligence

Long story short, I have an office that is in a industrial complex

One day my toilet was overflowing randomly I had thought that maybe it was our fault. So i called a plumber. But then the water turned pink and smelled like chemicals.

When the plumber came he thought this was odd and wondered if any if our neighbors had the same issue

Turns out we have a shared plumbing route with our neighbors who deal with paints and chemicals and they had been flushing chemicals down their toilet. The neighbors tried to stop us from investigating further but the plumber was able to take a sneak at their bathroom before getting kicked out and he saw their bathroom completely wrecked.

Our carpet was wrecked and is contaminated with sewage because it seeped into our main room. Im assuming we are going to have to get it steamed and the office decontaminated. We also had to pay the plumber over $900.

How do we go about getting reimbursed? What steps should I take to make sure our neighbors can compensate us fairly?

I just want to get back to work and the stench is horrible and I feel sick from inhaling the chemical fumes and sewage.

Thanks for reading!